1. Field of the Invention
The disclosed embodiments of the present invention relate to an optical disc drive, and more particularly, to a detecting method that checks if a voltage of a limit switch of an optical disc drive is changed to a high/low level to detect the action of the limit switch.
2. Description of the Prior Art
An optical disc drive accesses data of an optical disc by rotating the optical disc with high speed. To avoid damaging the optical disc, it is necessary to judge correctly that the loaded optical disc has arrived at the right position before rotating the optical disc. Moreover, to ensuring the safety in use, it is also necessary to confirm that the optical disc drive is ready for disc ejection before allowing the optical disc drive to eject the loaded optical disc.
Please refer to FIG. 1 together with FIG. 2. FIG. 1 is a diagram illustrating a cross-section of a conventional optical disc drive 1. Sub-diagrams in FIG. 2 illustrate voltage variations of a limit switch of the conventional optical disc drive 1. A tray 3 is disposed inside a hollow enclosure 2 of the conventional optical disc drive 1, a panel 4 is disposed in front of the tray 3 to shield an opening of the enclosure 2, and an ejection button 5 is disposed on the panel 4. An optical disc 6 is loaded on the tray 3, and the tray 3 may slide in or slide out through the opening of the enclosure 2. A spindle motor 7 is disposed in the center of the tray 3 to clamp and rotate the optical disc 6, and a pick-up head 8 is also disposed for moving back and forth along the radial direction of the optical disc 6 for accessing data of the optical disc 6. One end of a cable 9 is connected to the back of the tray 3, and the other end of the cable 9 is connected to a motherboard 10 disposed at the back of the inner side of the enclosure 2. A limit switch 11 is disposed on the motherboard 10. An elastic element 12 is disposed at the back end of the tray 3, and a locking device 13 is disposed at the lower edge of the front end of the tray 3. An electrical valve 14 is linked to the locking device 13 for hooking or releasing a latch 15 disposed on the enclosure 2.
When a disc loading process begins, the tray 3 carries the optical disc 6 and moves into the enclosure 2, and then the back end of the tray 3 presses the elastic element 12 such that the locking device 13 hooks the latch 15 and the tray 3 is locked in the enclosure 2. Meanwhile, the bottom of the tray 3 presses the limit switch 11 and then activates the limit switch 11. As shown in the sub-diagram (a) in FIG. 2, a voltage of the limit switch 11 is changed from a high level representative of a release status to a low level representative of an action status. Upon detecting that the voltage of the limit switch 11 is at the low level, the disc drive 1 confirms that the optical disc 6 has arrived at the right position, and then completes a disc loading process. Regarding a disc ejecting process, a user may manually push the ejection button 5 to make the voltage of the limit switch 11 changed from the low level to the high level, or the optical disc drive that completes an access command may automatically make the voltage of the limit switch 11 changed from the low level to the high level. As the optical disc drive 1 detects that the voltage of the limit switch 11 is at the high level and thus confirms that ejecting the loaded disc is needed, the disc ejecting process is completed. Meanwhile, the electrical valve 14 makes the linked locking device 13 released from the latch 15, and allows the elastic element 12 to eject the tray 3 from the enclosure 2. As a result, the bottom of the ejected tray 3 releases the limit switch 11, and the voltage of the limit switch 11 maintains the high level.
However, the limit switch 11 of the conventional optical disc drive 1 is very likely to be contaminated or oxidized by the suspended particles in the air, resulting in an abnormal voltage bouncing phenomenon of the voltage of the limit switch 11, as shown in sub-diagram (b) in FIG. 2. The voltage bouncing phenomenon occurs more often when the optical disc drive operates in the high temperature/humidity environment, or in a car driving environment with violent shaking. When the voltage of the limit switch 11 bounces, the optical disc drive which has completed the disc loading process misjudges that it needs to eject the loaded optical disc once detecting the voltage of the limit switch of the optical disc drive changed to the high level, and then stops disc access immediately to begin the disc ejecting process, which makes the optical disc drive load and eject the optical disc frequently and affects the access reliability and efficiency of the optical disc drive. Therefore, detection of the voltage status of activation or release of the limit switch in the conventional optical disc drive still has problems to be solved.